1. Field of the Invention
This invention relates to the manufacture of magnetic heads used in magnetic storage devices such as disk drives and tape drives. More particularly, the invention is directed to an improved lapping apparatus that reduces or eliminates rocking motion during the lapping of magnetic head wafers comprising multi-slider row bars.
2. Description of the Prior Art
By way of background, the conventional fixturing of a magnetic head wafer workpiece for lapping can lead to an undesirable condition known as crowning. Crowning occurs when the row bar surface being lapped is allowed to rock during lapping, thus creating unwanted facets. FIGS. 1–4 (not to scale) are illustrative. These figures show a workpiece 2 secured in a lapping carrier 4 (sometimes referred to as a “magazine”) that is in turn slidably mounted in a reference fixture 6 (sometimes referred to as a “nest”). The workpiece 2 is assumed to comprise a matrix of individual slider units arranged in a plurality of row bars. In FIG. 1, the row bars extend in a direction that is perpendicular to the plane of the figure. In FIG. 2, the row bars extend in a horizontal direction.
The reference fixture 6 has a set of support pads 8 on the bottom thereof that rest on the surface of a lapping element 10. This arrangement allows the reference fixture 6 and the lapping carrier 4 to move up and down, and thereby follow the lapping element's surface contour. The reference fixture 6 includes a vertically-walled aperture 12 that slideably receives the lapping carrier 4. In order to properly orient the workpiece 2 relative to the surface of the lapping element 10, a lateral force “LF” is applied to the lapping carrier 4 such that it is urged against positioning pads 14 extending from one of the walls of the aperture 12. The pads 14 serve as vertical reference surfaces for the lapping carrier 4. As shown in FIG. 1, there are three positioning pads 14 extending from the left vertical wall of the aperture 12. The lateral force LF is applied by way of a plunger actuator 15 or other force-imparting element (e.g., a spring). A downward force “DF” is also applied to the lapping carrier 4 to urge the lapping face of the lowermost row bar against the lapping element 10. As shown in FIGS. 2 and 2A, the downward force DF is applied using transducers 16 that engage a loading frame 17 placed over the lapping carrier 4. To ensure that no lateral forces are imparted to the lapping carrier 4, the transducers 16 have spring-loaded ball elements 18 that engage polished surfaces 19 on the loading frame 17. FIG. 2 also shows the use of additional positioning pads 14 on the ends of the lapping carrier 4.
FIG. 1 is representative of ideal conditions wherein the plunger 15 at all times urges the lapping carrier 4 against the pads 14. In this position, the workpiece lapping face 18 maintains a constant angle relative to the lapping element 10. Unfortunately, as shown in FIG. 4, frictional forces imparted by the lapping element 10 to the workpiece 2 can overcome the lateral force LF and cause the lapping carrier 4 to pivot away from its home position against the pads 14. This produces the crowning effect referred to above.
In the fixture of FIGS. 1–4, crowning can be corrected by increasing the lateral force LF imparted to the lapping carrier 4 by the plunger 15. The problem with this standard technique for controlling crowning is that friction is increased between the lapping carrier 4 and the pads 14. This increased friction opposes the downward force DF applied to the lapping carrier 4 by the transducers 16, and can cause the lapping carrier to rotate about an axis that is perpendicular to the plane of FIG. 2, as shown by the arrows “R.” This will result in non-uniform lapping across the row bar being lapped.
It is to improvements in the lapping of magnetic head wafer modules that the present invention is directed. In particular, what is needed is a lapping system design that effectively controls crowning without increasing the downward forces required to produce a required lapping force or introducing non-uniform lapping effects.